The present invention relates to a charge transfer device, and more particularly to a charge transfer device provided with a charge detection circuit of floating gate system.
For the charge detection at the output stage of a charge transfer device (which will be called "CTD" hereinafter), the floating diffusion system or the floating gate system is ordinarily employed. The floating diffusion system advantageously provides a large voltage gain at the output stage of the CTD, but has the drawback that signal charges are broken at the time of detection, thus making it impossible to successively transfer the charge which has been detected once. Contrary to this, while the drawback with the floating gate system is that step-up capacitor is generally required because transfer without loss to the subsequent stage is conducted, thus making it difficult to ensure the voltage gain as compared to the floating diffusion system, the advantage therewith is that because nondestructive charge detection is possible signals can be detected from several portions in the middle of the transfer unit.
However, CTDs using such a floating gate system give rise to the problem that signals detected through floating gates are caused to interfere with other signals, resulting in occurrence of crosstalk. This comes into question particularly in the case where floating gates are provided at a plurality of portions of the transfer path to conduct charge detection therefrom. This is because crosstalk occurs between detection signals from the plurality of portions. In addition, CTDs using the floating gate system and the floating diffusion system in combination also give rise to the problem that crosstalk occurs between detection signals based on the respective systems.